Tutorial Proggraming Free

tutorial - Howto create a MySQL user

Here is a quick tip how to create from mysql new database and a new mysql user that has full privileges on this newly created database:

mysql -uroot -p

CREATE DATABASE ;
GRANT ALL PRIVILEGES ON .* TO 'my_user'@'localhost' IDENTIFIED BY 'my_password' WITH GRANT OPTION;

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source:http://linuxpoison.blogspot.com/2008/05/13578175801652.html

tutorial - Howto open port using iptables

If you want your machine to respond to requests initiated from elsewhere on the internet, in effect to be a server, you need to open the required ports. To do this properly, you need to know:

1. What service you want to open up?
2. Whether it is a tcp or udp service?
3. What port number(s) it uses?

You may also wish to think about restricting access to certain machines; e.g. if you only want people in the X dept to access the machine.

For example, to enable ssh access to your box from anywhere on campus, you could use something like

iptables -A allowed -p tcp --dport 22 -s 129.2.0.0/16 -j ACCEPT
iptables -A allowed -p udp --dport 22 -s 129.2.0.0/16 -j ACCEPT

iptables -A allowed -p tcp --dport 22 -s 128.8.0.0/16 -j ACCEPT
iptables -A allowed -p udp --dport 22 -s 128.8.0.0/16 -j ACCEPT

This allows both udp and tcp traffic from either of the two class B networks to access port 22 on your machine. Of course, you need to have an sshd daemon running as well for this to work; the code above merely punches the required holes in the firewall.

source:http://linuxpoison.blogspot.com/2008/05/13578175807328.html

tutorial - ICMP Error codes

The Internet Control Message Protocol (ICMP) is one of the core protocols of the Internet protocol suite. It is chiefly used by networked computers' operating systems to send error messages—indicating, for instance, that a requested service is not available or that a host or router could not be reached, the below are the 16 error codes for ICMP.

0 - Network unreachable - Tells you if a specific network is currently unreachable.

1 - Host unreachable - Tells you if a specific host is currently unreachable.

2 - Protocol unreachable - This code tells you if a specific protocol (tcp, udp, etc) can not be reached at the moment.

3 - Port unreachable - If a port (ssh, http, ftp-data, etc) is not reachable, you will get this message.

4 - Fragmentation needed and DF set - If a packet needs to be fragmented to be delivered, but the Do not fragment bit is set in the packet, the gateway will return this message.

5 - Source route failed - If a source route failed for some reason, this message is returned.

6 - Destination network unknown - If there is no route to a specific network, this message is returned.

7 - Destination host unknown - If there is no route to a specific host, this message is returned.

8 - Source host isolated (obsolete) - If a host is isolated, this message should be returned. This code is obsoleted today.

9 - Destination network administratively prohibited - If a network was blocked at a gateway and your packet was unable to reach it because of this, you should get this ICMP code back.

10 - Destination host administratively prohibited - If you where unable to reach a host because it was administratively prohibited (e.g., routing administration), you will get this message back.

11 - Network unreachable for TOS - If a network was unreachable because of a bad TOS setting in your packet, this code will be generated as a return packet.

12 - Host unreachable for TOS - If your packet was unable to reach a host because of the TOS of the packet, this is the message you get back.

13 - Communication administratively prohibited by filtering - If the packet was prohibited by some kind of filtering (e.g., firewalling), we get a code 13 back.

14 - Host precedence violation - This is sent by the first hop router to notify a connected host, to notify the host that the used precedence is not permitted for a specific destination/source combination.

15 - Precedence cutoff in effect - The first hop router may send this message to a host if the datagram it received had a too low precedence level set in it.

source:http://linuxpoison.blogspot.com/2008/05/135781758012188.html

tutorial - Time bases iptables rules

Question: How can I restrict/allow access to certain service on timely basis with iptables? For example restrict access to SSH between 7:00 pm - 8:00 am on weekdays?

Answer: You are welcome to use iptables patch-o-matic extension (pom or p-o-m) that allows you to match a packet based on its arrival or departure (for locally generated packets) timestamp. The syntax is the following:

iptables RULE -m time --timestart TIME --timestop TIME --days DAYS -j ACTION

Where:

--timestart TIME: Time start value (format is 00:00-23:59)
--timestop TIME: Time stop value (the same format)
--days DAYS: a list of days to apply, from (format: Mon, Tue, Wed, Thu, Fri, Sat, Sun).

To add the rule stated in the question use the following command:

iptables -A INPUT -p tcp -d 192.168.0.1 --dport 22 -m time --timestart 19:00 --timestop 8:00 -days Mon,Tue,Wed,Thu,Fri -j DROP

Hope it helps!

[source: http://www.linuxscrew.com/]

source:http://linuxpoison.blogspot.com/2008/05/13578175808226.html

tutorial - GUI tools to build Iptables/Firewall rules

fwbuilder

Firewall Builder is a GUI firewall configuration and management tool that supports iptables (netfilter), ipfilter, pf, ipfw, Cisco PIX (FWSM, ASA) and Cisco routers extended access lists. Firewall Builder uses object-oriented approach, it helps administrator maintain a database of network objects and allows policy editing using simple drag-and-drop operations.

It is run on a separate host system, where you create the policy files, and then copy them over and run them on the target system. It is able to handle everything from very simple rulesets to large and rather complicated ones. It has extensive abilities to handle different versions and installations of iptables, by configuration of which targets/matches are available on each host system, etcetera. The end result may be saved in an parsable configuration file (e.g., the real firewall scripts).

fwbuilder can be found at http://www.fwbuilder.org.

Turtle Firewall Project

Turtle Firewall is a software which allows you to realize a Linux firewall in a simply and fast way.
It's based on Kernel 2.4.x/2.6.x and Iptables. Its way of working is easy to understand: you can define the different firewall elements (zones, hosts, networks) and then set the services you want to enable among the different elements or groups of elements.
You can do this simply editing a XML file or using the comfortable web interface Webmin.

You can find the Turtle Firewall Project and more information over here

Easy Firewall Generator for IPTables

Easy Firewall Generator is another interesting development when it comes to iptables and netfilter. Basically, Easy Firewall Generator is a PHP webpage where you specify options and specifics of your firewall, and once all of the configurations are done, you click a button, and the webpage spits out an iptables ruleset that you can utilize.

The script contains all the basic rules, and more specific ones to contain strange patterns in packets. It also contains specific IP sysctl changes that may be needed, loads necessary modules, et cetera. The whole ruleset is also written in a redhat init.d format.

source:http://linuxpoison.blogspot.com/2008/05/135781758012037.html

tutorial - What is 127.0.0.1?

27.0.0.1 is the standard IP address used for a loopback network connection.

This means that if you try to connect to 127.0.0.1, you are immediately looped back to your own machine. If you telnet, ftp, etc... to 127.0.0.1, you are connected to your own machine.

In other words, 127.0.0.1 is you.

For example, if your system was named "hostname", and you attempted to telnet to 127.0.0.1, you would see:

# telnet 127.0.0.1
Trying 127.0.0.1...
Connected to hostname
Escape character is '^]'.

Another name for 127.0.0.1 is localhost.

Although 127.0.0.1 is the most commonly utilized address for localhost, any IP address in the 127.*.*.* range should also function in the same manner.

source:http://linuxpoison.blogspot.com/2008/05/135781758013735.html

tutorial - Install multimedia Support in Fedora 9

Follow these instructions to get mp3 and other multimedia support on your Fedora Core 9.

Open a terminal and become root, then run this command:

# wget http://livna-dl.reloumirrors.net/fedora/9/i386/livna-release-9-1.noarch.rpm
# rpm -ivh livna-release-9-1.noarch.rpm

Install all other multimedia plug ins..

# yum -y install gstreamer-plugins-bad gstreamer-plugins-ugly xine-lib-extras-nonfree

source:http://linuxpoison.blogspot.com/2008/05/135781758012268.html

tutorial - Kernel oops count

If you want to know what is kernel oops:
An oops is a deviation from correct behavior of the Linux kernel which produces a certain error log. The better-known kernel panic condition results from many oops, but others may allow continued operation with compromised reliability.

When the kernel detects a problem, it prints an oops message and kills any offending process. The message is used by Linux kernel engineers to debug the condition which created the oops and fix the programming error which caused it.

Once a system has experienced an oops, some internal resources may no longer be in service. Even if the system appears to work correctly, undesirable side effects may have resulted from the active task being killed. A kernel oops often leads on to a kernel panic once the system attempts to use resources which have been lost.

There is an website which counts this oops : http://www.kerneloops.org/

kerneloops.org is a website that tries to help the developers of the Linux kernel by collecting so-called oopses, which are the crash signatures of the Linux kernel. The collected oopses are processed statistically to present information for the kernel developers, such as

* Which crash signatures occur the most? (and thus need to be fixed most urgently)
* When did a certain crash signature show up first?
* Which API functions are the most error prone?

Fedora 9 have a process to send this oops to this site.

source:http://linuxpoison.blogspot.com/2008/05/13578175805758.html

tutorial - Moonlight (silverlight for linux) relesead

Moonlight is an open source implementation of Microsoft Silverlight for Unix systems.

Mono provides the necessary software to develop and run .NET client and server applications on Linux, Solaris, Mac OS X, Windows, and Unix. Sponsored by Novell (http://www.novell.com), the Mono open source project has an active and enthusiastic contributing community and is positioned to become the leading choice for development of Linux applications.

First Moonlight Source Code Release

To encourage users to try out Moonlight, we are doing a source-code only release of Moonlight for developers to try out Moonlight.

To try out Moonlight, you have two options:

* Media codecs: you must do your own build from source code.
* No-media codecs: we provide one-click addins for Firefox that will install with no effort.

Firefox addins are available from http://www.go-mono.com/moonlight.

Source code for Moonlight is available from here. To compile Moonlight from source code follow these instructions.

source:http://linuxpoison.blogspot.com/2008/05/13578175802645.html

tutorial - Install multimedia Support in Ubuntu Hardy Heron

The below commands downloads all the required codecs from the Medibuntu repositories and enble the full multimedia support for your Ubuntu box, now with this you can play the encrypted DVD playback, Adobe Flash and non-native media files (Windows media, Apple QuickTime, Real, MP3).

Open the terminal

sudo wget http://www.medibuntu.org/sources.list.d/hardy.list -O /etc/apt/sources.list.d/medibuntu.list
sudo apt-get update
sudo apt-get install medibuntu-keyring
sudo apt-get update
sudo apt-get install libdvdcss2 w32codecs

source:http://linuxpoison.blogspot.com/2008/05/13578175808747.html

tutorial - Restricting scheduling (cron, at) to normal user

If you run a system that hosts multiple users, you might want to discourage them from using cron or at for whatever reasons. This can be done.

To restrict people from using cron, create a file called /etc/cron.deny and put the name of the user you want to restrict in there.

To restrict people from using at, create a file called /etc/at.deny, and put the name of the user you want to restrict in there. Be careful about restricting default system users like nobody. These accounts sometimes run their own jobs at specific times.

source:http://linuxpoison.blogspot.com/2008/05/13578175802310.html

tutorial - Posfix security - How to change mailbanner

By default the installation of Postfix is already security-minded. An out-of-the-box install could be enough for most users but still, some tweaking could not hurt.

Replace your mailbanner (the text one sees when telnetting to your port 25) with something meaningless.
This is what you see when you do telnet to port 25.

nikesh@poison:~> telnet localhost 25
Trying 127.0.0.1...
Connected to localhost.
Escape character is '^]'.
220 poison.hell.com ESMTP Postfix

Now to remove this banner incformation, you need to change a variable setting in your main.cf file, something like ...

smtpd_banner = $myhostname ESMTP Sorry, No banner

After doing the change, restart your postfix server and try doing telnet again to port 25

nikesh@poison:~> telnet localhost 25
Trying 127.0.0.1...
Connected to localhost.
Escape character is '^]'.
220 poison.hell.com ESMTP Sorry, No banner

source:http://linuxpoison.blogspot.com/2008/05/13578175809031.html

tutorial - What is TCP reset attacks

The primary idea behind a TCP reset attack is to falsely terminate an established TCP connection. Lets imagine an established TCP connection from host A to host B. Now, a third host, C, spoofs a packet that matches the source port and IP address of host A, the destination port and IP address of host B, and the current sequence number of the active TCP connection between host A and host B. Host C sets the RST bit on the spoofed packet, so when received by host B, host B immediately terminates the connection. This results in a denial of service, until the connection can be reestablished. However, the severity of such an attack is different from application to application.

source:http://linuxpoison.blogspot.com/2008/05/13578175804777.html

tutorial - What are Sticky Bit, SUID (Set User ID) Bit and SGID (Set Group ID) Bit

Sticky Bit

Setting the sticky bit tells Unix that once the concerned application is executed, it should remain in memory. Remember that Unix is a multi-user OS and was mainly designed so that multiple users can work simultaneously. Thus the logic used is that a program that exists in memory requires lesser time to start when a new user requests for the same program. Thus when one user has just used a program and then a new user wants to use the same program, the second user doesn't have to face a time delay for the program to initialize itself. It would be readily available to him. The concept of the sticky bit was a very useful one, long back when fast disk access and other memory access technologies weren't around. But in today's age the concept of sticky bit is obsolete, since modern day technology is advanced enough to reduce the time delay while loading applications into the memory. Thus currently the sticky bit is of very little significance. Sticky bit is only associated with executables.

SUID (Set User ID) Bit

Sometime you may faced an error while trying to run any application stating that the application must be 'SUID root' . You might have been confused that time, but now once you read this article you would no longer find it confusing.

SUID stands for Set User ID. This means that if the SUID bit is set for any application then your user ID would be set as that of the owner of application/file rather than the current user, while running that application. That means in case I have an application whose owner is ' root ' and it has its SUID bit set, then when I run this application as a normal user, that application would still run as root. Since the SUID bit tells Linux that the the User ID root is set for this application and whenever this application executes it must execute as if root was executing it (since root owns this file).

In case you have really understood the above you may be wondering - isnt this a major security risk? If users are able to run applications as root, then it must be definitely posing as a threat to the security of the system. Actually the SUID is used to increase the security in a way. Let me explain this with my own example I use on my machine.

SGID (Set Group ID) bit

Just like SUID, setting the SGID bit for a file sets your group ID to the file's group while the file is executing. IT is really useful in case you have a real multi-user setup where users access each others files. As a single homeuser I haven't really found a lot of use for SGID. But the basic concept is the same as the SUID, the files whose SGID bit are set would be used as if they belong to that group rather than to that user alone.

source:http://linuxpoison.blogspot.com/2008/05/135781758019814.html

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